This invention relates to a non-linear stair, that is a stair having at least part thereof which is curved and thus extends from the bottom of the stair to a top of the stair over a non-linear path.
The major attraction about curved stairs of this type is that they are architecturally and visually very appealing and to achieve the maximum visual appeal it is preferable if they are custom designed to obtain a particularly unique shape. It will be appreciated, however, that stairs of this type require considerable amount of skill and long labour and accordingly are extremely expensive. Traditionally such curved or non-linear stairs are manufactured by the following steps:
(1) First the number of risers and their height has to be determined (usually 14 risers for standard 8' ceiling height). PA0 (2) A drawing scale 1-1 has to be done showing all the treads, the stringers and risers. The number of treads to be one less than the number of risers. PA0 (3) Then the treads are made by transferring the lines, angles and curves from the drawing onto an oversized piece of wood making the ends approximately 1/2" longer than the inside edge of the stringers so they can be mortised into the stringers. Also each tread has to be made wider at the front edge by a predetermined size so that every consecutive tread overhangs the previous one. This is called a nosing and allows for moulding or carpet to be wrapped around. Then the treads are grooved to house the top edge of the risers. PA0 (4) Next the riser is made by marking the inside stringer line of both stringers at the front and back of each riser which will give the angle at which they have to be cut, the riser being a board equal in size to the rise previously determined plus depth of groove in the treads. Again the riser has to be cut 1/2" longer on each end to be mortised into the stringers. PA0 (5) Next the stringers have to be laid out on the inside from which the stringers are to be laminated. Great care must be taken that all measurements correspond exactly with the drawing because these markings are used to mortise the stringers after they are laminated to house the treads and risers. PA0 (6) Next a form has to be made for each stringer. This is usually done in the following manner: PA0 (7) After the stringers are completed the stairs can be assembled by starting with riser and tread #1, inserting them into the grooves or cut outs of the stringers and insert every other consecutive riser and tread in the same manner. The treads and risers are affixed to the stringers by various means such as glue and nails, screws, bolts, dowels or wedges. PA0 forming a plurality of treads having a required shape to follow the path, PA0 forming a first and a second board each of which has a length to extend along a respective one of the stringers and a height substantially equal to the transverse dimension of the respective stringer, each of said boards being sufficiently flexible to bend into the shape of the respective stringer without fracturing, PA0 attaching the treads to each of the boards at required positions thereon for the treads and boards to follow the path, PA0 and subsequent to said attaching step laminating onto each of said boards further layers to build up to a required stringer thickness. PA0 said boards being attached to the treads at required positions thereon for the treads and boards to follow the path, PA0 and subsequent to said attachment having laminated thereon further layers to build up to a required stringer thickness.
Depending on the height of the stair, 4 or more horizontal frame members have to be made, usually from 11/2" plywood. They also have to be made wide enough to hold their shape. These members have to be made to correspond with the inside line of the stringers less the size of the vertical members which will have to be mounted up on them at approximately 6" intervals, the members usually being 2.times.4 on the edge. Then all the vertical members have to be attached to the horizontal members. By now the form looks like part of a cage. Before this large form can be set up-right it has to be substantially braced to hold it square. When in upright position the form must be plumbed in al directions and braced securely because accuracy is important so the curvature and shape of the stringers match the treads and riser. To allow laminating the form must be able to support several hundred pounds of weight. Once the forms are set up and secured the upright members must be marked for the #1 riser ad read as well as the #13 tread and # 14 riser also #7 tread should be marked to avoid sagging. Then the inside layers of the stringers which have previously been laid out are bent into the form making sure tread #1, #7 and #13 as well as risers #1 and #14 match up exactly. The inside stringer layer can be held in place with finishing nails. Then subsequent layers of plywood are glued and clamped on the top of each other until the desired thickness of stringer is reached. Then stringers are left in the forms for about 24 hours for curing before they can be processed further. After curing, the stringers are trimmed, that means the ends are cut to desired lengths and angles also the edges have to be trimmed flush and square. Next the stringers have to be mortised usually by using a router bearing in mind that the stringers are curved one concave and one convex. Special router guides have to be used and great skill is required. To finish of mortising the ends of the grooves have to be finished off by hand using a chisel and hammer to match the groove to the moulding at the front of the tread as well as back edge where the tread and the riser meet. All the work performed on the stringers is time consuming because they are shaped like a corkscrew and it is difficult to hold them down and they constantly have to be reclamped.
The above procedure applies to both the housed stringer as well as the open stringer type. Stringers for open end stairs are not mortised, they have to be cut out for the treads to lay on which is very tedious and time consuming because accuracy is important to assure all the treads and risers fit well. Because of the curvature of the stringers, machines cannot be used.
It will be appreciated, therefore, that much of the labour involved in the manufacture of stairs by the conventional technique is involved in manufacturing the framework necessary for forming the stringers and for supporting the stringers and the treads during their assembly. This is therefore a highly inefficient manufacturing technique and significantly increases the cost of such custom built stairs.
The frame needs to be custom built for each different size and shape of stair and when large numbers of different sizes and shapes are to be built, the frame cannot be maintained and stored for future use as the number of different frames is of course very large.
Some manufacturers overcome this difficulty by limiting the stairs which they manufacture to a number of specific shapes and dimensions and in this way they are able to manufacture curved stairs more economically. However they are unable to build different shapes and dimensions of stairs according to the requirements of a particular customer and this leaves a significant market for custom built stairs which is totally unfulfilled.
It is one object of the present invention, therefore, to provide an improved method of manufacturing a non-linear stair which enables the manufacture of custom designed stairs without the necessity for a supporting frame arrangement.